The overall goals of this grant are: (1) to develop methods based on structural studies and in vitro production of erythropoietin (ESF) which can lead to the acquisition of hormone suitable for therapeutic use, (2) to develop ESF assay methods which can be of use in enhancing clinical studies and the investigation of erythroid kinetics. During the last grant year: (1) the fetal mouse liver assay for erythropoiesis stimulating activity (ESA) was established in this laboratory; (2) lectins have been used to aid in the purification of ESF; (3) synthetic surface reactive microspheres have been used as indicators in place of red blood cells in the agglutination inhibition assay; (4) 39 kidney and liver cell lines have been studied for erythropoietin production; (5) a study of ESF levels in pregnancy was started; and (6) an investigation of ESA levels in unstressed dogs was completed and cyclic variations were found. During the next grant year, the objectives include: (1) the production on monospecific antibodies to erythropoietin; (2) initiation of work on immunoradiometric assay of erythropoietin; (3) utilization of electron microscopic methods to identify cellular sites of production and reception of erythropoietin; and (4) examination of the bone marrow erythroid series of cyclic hematopoietic dogs throughout their cycle by both light microscopy and electron microscopy.